Request for review: JEP: GC Interface: Better isolation of GC implementations

Erik Helin erik.helin at
Thu Nov 17 14:08:39 UTC 2016

On 11/15/2016 07:02 PM, Roman Kennke wrote:
> Hi all,
> No comments on that one?

Hi Roman,

sorry, I must have missed your email the first time, thanks for sending 
out a reminder.

I think the overall approach you have outlined in the JEP is really 
good, this is something I've wanted for a long time. We don't have to 
get into all the gritty details to start with, but I have few initial 
comments on your approach:

- why does the GCInterface need to include an implementation of
   AdaptiveSizePolicy? Right now, the only common interface for all the
   GC algorithms is CollectorPolicy. Why should it be required to
   implement an AdaptiveSizePolicy?
- the part about MemoryService, the memory pools, etc. is great, that
   code is a mess today.
- regarding your questions on where the barrier code for the JITs (C1,
   C2) should be kept, I think I would prefer to have it in
   src/share/vm/opto (for C2 code), but have it in a separate file. Have
   you given any thought to JIT code other than the actual barriers? For
   example passes in C2 that are only needed for a particular GC.

I also discussed your ideas around the BarrierSet with Erik Österlund, 
our template guru :) I think Erik has few ideas in this area, but I will 
let Erik describe his thoughts.

On a more general note, is the patch at up to date? 
If so, I will try to look through it and come back with some more 
feedback. Furthermore, is there any way this could be implemented as a 
series of patches (or as a branch in the jdk9/sandbox forest), to ease 


> I'd like to move it to 'submitted' if nobody objects.
> Roman
> Am Dienstag, den 16.08.2016, 19:37 +0200 schrieb Roman Kennke:
>> Hi all,
>> I would like to ask for your opinion on the JEP draft:
>> It was born out of the discussion around JEP 291: Deprecate the
>> Concurrent Mark Sweep (CMS) Garbage Collector, and the development of
>> the Shenandoah GC, both of which would benefit greatly from better GC
>> isolation.
>> Best regards, Roman

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